Considerable resources have been invested, by way of research time and money, in the study of replacing the heart, when in is diseased or otherwise failing, in order to prolong the productive life of the patient. Much progress has been made in "heart transplants", and less successful attempts have been made in providing a mechanical replacement for the heart. The major disadvantages with both these developments are well known.
More recently, developments have been made to provide a cardiac assister cup attached to the ventricles and to pump and withdraw air from the cup to assist during systole and diastole, the pulses being coordinated with the rhythm of the heart. This was described by Anstadt, G. L. et al, in "Prolonged Circulatory Support by Direct Mechanical Ventricular Assistance", Trans. ASAIO 12:72-79, 1966, and Skinner, D. B., in "Experimental and Clinical Evaluations of Mechanical Ventricular Assistance", The American Journal of Cardiology, 27:146, 1971. U.S. Pat. No. 4,192,293, Asrican, issued Mar. 11, 1980, also describes a cup or rigid sheath with a fluid expansible envelope for compressing the heart during systole.
Recent developments have also been made to utilize a skeletal muscle, which has been transformed to be fatigue resistant, wrapped around the heart in "dynamic cardiomyoplasty", as described in an article by Dewar, M. L. et al, entitled "Synchronously Stimulated Skeletal Muscle Graft for Myocardial Repair: An Experimental Study", Journal of Cardiovascular Surgery, 87:325, 1984, and the first successful case was reported by A. Carpentier et al in an article entitled "Myocardial Substitution with a Stimulated Skeletal Muscle: First Successful Clinical Case", Lancet 8440:1267, 1985. In dynamic cardiomyoplasty, the latissimus dorsi muscle pedicle is wrapped around the heart, and the muscle is stimulated by an implanted battery-operated, electric pulse device in order to contract the muscle in synchrony with cardiac systole.
Circulatory counterpulsation with the intraaortic balloon is a widely accepted form of cardiac assist. Recently, reports of extended support with the balloon pump have confirmed its efficacy in chronic situations. In several cases, patients were supported from weeks to almost a year. Many more patients with end-stage failure could benefit from chronic counterpulsation support. A major limitation is the patient's dependency on an external power source with its risk of infection and restriction in mobility. A totally implantable counterpulsation assist system would offer an important therapeutic option for patients with end-stage heart failure.
Recent advances in technology and skeletal muscle biology now allow for a viable alternative source in cardiac assistance. It has been demonstrated that skeletal muscle can be made fatigueresistant and powerful enough to continuously assist the heart.
A totally implantable muscle-powered counterpulsation device should have many clinical applications. It could be useful for patients with frequent or chronic heart failure but with some remaining . cardiac function, so that they are not candidates for heart transplantation or artificial heart devices. As a bridge to transplantation, such a device has the advantage of not being tethered to an external power source, so that infectious complications are avoided. The development of a new pulse-train (i.e., burst) stimulator that can summate the contraction pattern of a skeletal muscle to make it resemble that of the myocardium and to synchronize it precisely with the selected portion of the cardiac cycle is described in an article by Carlos M. Li et al, entitled "A New Implantable Burst Generator for Skeletal Muscle Powered Aortic Counterpulsation", published in ASAIO Transactions, July-September 1989, Vol. 35, No. 3, p. 405.
After connecting the balloon to the aorta so that it would be compressed by the latissimus dorsi muscle, the burst stimulator could stimulate the latissimus dorsi muscle during diastole to achieve significant diastolic augmentation.